The prior art exhaust muffler comprises an array of tubes disposed within an outer shell. The array of tubes defines at least one inlet and at least one outlet which extend through the outer shell of the muffler and enable the muffler to be connected into an exhaust system. Portions of the array of tubes within the typical prior art muffler are perforated to permit a controlled circulation of exhaust gases into an expansion chamber defined between the perforated tubes and the outer shell of the muffler. This circulation of gases into and/or through the expansion chamber contributes to the sound attenuation of the muffler.
The particular sound attenuation achieved by the prior art muffler depends upon a host of design parameters including the characteristics of the exhaust gases, the dimensions of the tubes within the muffler, the area of the perforations in the tubes and the volume of the expansion chamber. Some prior art mufflers include a plurality of expansion chambers of different engineering designs in an effort to attenuate specified ranges of noises. For example, a small chamber with a single perforated tube passing therethrough often is provided to attenuate a narrow, high frequency range of sounds, and is referred to as a high frequency tuning chamber.
Expansion chambers and high frequency tuning chambers often are not sufficient to achieve specified noise attenuation levels. More particularly, it is often found that a relatively narrow band of unacceptable noise exists despite properly engineered expansion chambers and high frequency tuning chambers. Most exhaust mufflers accommodate this residual noise with one or more tuning tubes and a corresponding number of low frequency resonating chambers. In this context, a low frequency resonating chamber is defined as a substantially enclosed chamber, and a tuning tube extends into the low frequency resonating chamber and is in communication with other tubes carrying exhaust gases from the inlet to the outlet of the muffler. Thus, the combination of a tuning tube and a low frequency resonating chamber performs a noise attenuation function, but no significant function in carrying exhaust gases between the inlet and outlet of the muffler. Low frequency resonating chambers and tuning tubes employ principles similar to those involved in playing a flute or blowing across the top of a bottle. In particular, the range of frequencies that will be attenuated by a low frequency resonating chamber is determined by the length and cross-sectional area of the tuning tube and the volume of the low frequency resonating chamber. In many instances, a plurality of functionally distinct low frequency resonating chambers will be required within an exhaust muffler to achieve specified noise levels.
The typical prior art muffler employs a plurality of separate tubes supported in generally parallel relationship on a plurality of transversely extending baffles. A sheet of metal is then wrapped into an oval or circular cross section to define an outer shell which envelopes the tubes and baffles. A pair of opposed heads then are secured to opposite ends of the tubular outer wrapper to complete the prior art muffler. The various chambers of the these prior art mufflers are formed between either the outer shell, a head and a baffle or between the outer shell and a pair of baffles. A typical prior art muffler of this general construction might include a total of four internal baffles which define an expansion chamber and two low frequency resonating chambers within the muffler. In certain unusual instances, the prior art muffler may require five transverse baffles to create the required number of chambers within the muffler.
The above described wrapped outer shell muffler is by far the most prevalent exhaust muffler employed on vehicles. However, there have been many efforts to develop mufflers with at least some stamp formed components. For example, U.S. Pat. No. 4,396,090 which issued to Wolfhugel on Aug. 2, 1983, shows an exhaust muffler with a pair of plates stamp formed to define an array of tubes, a plurality of transverse baffles to support the internal plates and to define chambers within the muffler and a wrapped outer shell. Other stamp formed mufflers consist of two stamp formed external shells configured to define a convoluted path through which exhaust gases may travel. These prior art mufflers include U.S. Pat. No. 2,484,827 which issued to Harley and U.S. Pat. No. 3,638,756 which issued to Thiele. Still other stamp formed mufflers have included a pair of stamp formed outer shells and one or more stamp formed internal components defining tubes and baffles within the outer shells. Examples of these mufflers are shown in British Patent No. 632,013 which issued to White in 1949; British Patent No. 1,012,463 which issued to Woolgar on Dec. 8, 1965; and U.S. Pat. No. 4,132,286 which issued to Hasui et al. on Jan. 2, 1979.
Japanese Patent No. 59-43456 shows one muffler formed substantially entirely with stamp formed components and another muffler formed with a combination of stamp formed and tubular components. Both embodiments shown in Japanese Patent No. 59-43456 include inserts mounted in selected tubes to divert portions of the exhaust gases through perforations downstream from the insert. Both embodiments also create chambers with folded flaps on the internal plates and/or with separate stamp formed baffles. The embodiment of Japanese Patent No. 59-43456 formed entirely with stamp formed components includes two chambers defined as resonance chamber. These resonance chambers communicate directly with a large expansion chamber, and not with any of the stamp formed tubes. In particular, this muffler does not include a tuning tube, the length and cross-sectional area of which partially determine the specific frequency of noise to be attenuated. The other embodiment shown in Japanese Patent No. 59-43456 does include a single resonance chamber with a stamp formed tuning tube. However, this embodiment requires the undesirable combination of stamp formed and tubular components to make the muffler functional.
The above identified copending patent applications describe several substantial improvements to mufflers formed from stamp formed components. In particular, copending application Ser. No. 934,642 shows several novel constructions for mufflers formed from three or more stamp formed members to yield an array of tubes, at least one expansion chamber and at least one low frequency resonating chamber. Similarly, copending patent application Ser. No. 061,876 and copending patent application Ser. No. 061,913 each show mufflers formed from stamp formed components which define an expansion chamber, a reversing chamber and a low frequency resonating chamber. In particular, copending application Ser. No. 061,876 shows a stamp formed muffler with efficient alignments of the inlet and outlet tubes. Copending application Ser. No. 061,913 shows several efficient constructions for the tubes and chambers within the stamp formed muffler.
Despite the many advantages offered by stamp formed mufflers in general, and in particular by the copending applications identified above, it has been found desirable to make further improvements in stamp formed mufflers. More particularly, it has been found desirable to provide mufflers having stamp formed components and having a plurality of low frequency resonating chambers.
In view of the above, it is an object to provide a muffler having stamp formed components and having a plurality of low frequency resonating chambers.
It is another object of the subject invention to provide a muffler having a plurality of low frequency resonating chambers without separate internal baffles.
It is an additional object of the subject invention to provide an exhaust muffler with a plurality of low frequency resonating chambers without the formation of additional convolutions or chambers within the outer shell of the muffler.